Using ultrasounds for the estimation of the misalignment in plate–plate torsional rheometry

Abstract

A new method to accurately quantify the gap error arising from non-parallelism in plate–plate and cone–plate torsional rheometry is proposed. This method consists in monitoring the ultrasonic pulses sent by a transducer adapted to the rheometer bottom plate. The time of flight (TOF) of the echoes reflected by the rheometer upper plate, while it rotates at small angular velocity having a sample placed between the plates, is measured. As the sample acoustic velocity is constant and known, any variation in the TOF is correlated with changes in the distance between plates and thus, the misalignment is automatically determined.